P. Bai

Effect of substrate surface roughness on the columnar growth of Cu films

Vapor‐deposited films prepared under low adatom mobility conditions commonly exhibit columnar structures. We present the scanning electron microscopy study of Cu films with a thickness around 3.7 μm deposited on rough Al2O3 ceramic substrates and smooth SiO2 substrates. The Cu films were deposited using the partially ionized beam deposition technique under the same deposition conditions. The films deposited on the rough substrates have a typical columnar structure while those deposited on the smooth substrates are noncolumnar. The complete difference in physical structures is due to the difference in the substrate surface roughness. The results indicate that in any structure zone model for the physical structure of the film the substrate surface roughness is an important parameter and cannot be neglected. It is reasoned that the adatom surface diffusion length, which is determined by the deposition conditions, serves as a critical measure for the length scale of surface roughness. At the initial stage of ...

Low‐resistivity Cu thin‐film deposition by self‐ion bombardment

An anomalous reduction of the thin‐film resistivity has been observed in the Cu deposition at room temperature using a partially ionized beam in which the self‐ions are used to bombard the substrate surface during growth. A minimum thin‐film resistivity of 1.83 μΩ cm has been obtained at 2 kV substrate bias voltage with an ion percentage of about 1% in the beam for films of 2500 A thickness. This is compared to the resistivity of close to 4 μΩ cm obtained by the conventional evaporation technique without the use of self‐ions. We discuss the results within the framework of the theory of grain‐boundary resistivity proposed by Mayadas and Shatzkets [Phys. Rev. B 1, 1382 (1970)].

Deposition of Cu film on SiO2 using a partially ionized beam

Ion bombardment during deposition can significantly modify the film properties. In the partially ionized beam deposition, ions derived from the depositing material, i.e., the self‐ions, are used during deposition. Cu films were deposited on SiO2 substrates at room temperature using 1% Cu self‐ions with an energy ranging between 0–4 keV. We studied the microstructures of the Cu films using x‐ray diffraction and transmission electron microscopy, measured the impurity level inside the films using secondary ion mass spectrometry, and performed the resistivity measurements using a four point probe. The results indicate that there is an optimum ion energy around 2 keV at which, the integrated x‐ray intensity ratio I(111)/I(200) reaches its maximum value indicating a strong 〈111〉 texture, while the impurity concentration and resisitivity are minimum. The correlation between the structural, compositional and electrical properties are discussed in the framework of Mayadas and Shatzkets’s theory of grain boundary r...

Diffusion in Ni/Cu bilayer films

It is shown that the diffusion of Cu into the Ni layer of a Ni/Cu bilayer film after thermal annealing is significantly reduced when the deposition temperature of the Ni layer is raised from approximately 50 to 200 °C. The effect of the deposition temperature on the physical structure of the Ni layer and the possible connection between the Ni layer physical structure and the diffusion reduction are investigated. The effect of the diffusion on the resistivity of the Cu layer is also studied.

Intrinsic Cu gettering at a thermally grown SiO2/Si interface

SiO2 film of 1500‐A thickness has been grown by a conventional thermal dry oxidation process on commercial Si(111) and Si(100) wafers. A secondary‐ion mass spectrometry study of the SiO2/Si structure showed that a gettering of Cu atoms, which were present in the Si wafers as residual impurities, has occurred at the SiO2/Si interface due to the thermal dry oxidation process. The areal concentration of the Cu atoms at the interface has been found to depend on the Cu concentration in the Si wafers. Areal concentrations in order of 1×1012/cm2 were measured at the interfaces. Facilitated by the high diffusivity of Cu in SiO2 and Si, the gettering is thermodynamically driven by the low solid solubility of Cu, either in SiO2 at the temperature range up to the oxidation temperature, or in Si at low temperatures as the wafers cool down. The defects generated at the SiO2/Si interface provide the nucleation sites for the Cu gettering.

Formation of low‐temperature Al/n‐Si Schottky contacts using a partially ionized beam deposition technique

High quality Al/n‐Si Schottky contacts have been fabricated using the partially ionized beam (PIB) deposition technique in a conventional vacuum condition without post heat treatment. The electrical characteristics of the diodes were extremely uniform across a 3 in. wafer and were stable with respect to a furnance annealing performed at 450 °C for 30 min. Scanning electron microscope examination revealed much shallower pit formation on the Si surface, as compared to that deposited by conventional means, following the heat treatment. A completely smooth Si surface was observed after a 10 s rapid thermal annealing at 450 °C. The observed behavior could be attributed to the creation of ‘‘contact openings’’ in the native oxide during deposition by ion bombardment, allowing Al to make an intimate contact to Si. This PIB deposition of metal‐semiconductor contacts may be an important metallization scheme for the future low‐temperature processing of shallow junctions for very high speed integrated circuits.

Unusual orientation relationship for a copper film on Si(111)

The texture of a copper film deposited on bare Si(111) is studied. Deposition is done using the partially ionized beam technique where no potential is applied to the substrate. Pole figure analysis shows a very sharp texture where Cu{531} is parallel to Si(111). In the plane of the film, two variants of copper orientation are present with orientation relationships Si〈112〉//Cu〈134〉and Si〈112〉//2.5° from Cu〈350〉. The rotation between variants of 56.5° is less than the Cu(111) twin orientation. Possible reasons for the mismatch are discussed.

Effect of elemental plasma on metal/Si films by partially ionized beam deposition

The observation of surface cleaning during self-ion-assisted vacuum deposition of epitaxial Ag films on Si(111) is discussed. The details of the self-cleaning effect are then compared among the three metal/Si systems Ag/Si, Cu/Si, and Al/Si. The films were all grown at room temperature using a partially ionized beam (PIB) deposition system under high vacuum. The impurities C, O, and H were detected by secondary ion mass spectrometry. Reduction of these species both at the interface and in the films was observed due to the addition of ∼1-2% of 1-3 keV ions to the depositing beam. It was seen that for the Al case the cleaning effect was restricted more closely to the interface. It is argued that a possible origin of the enhancement of the cleaning in the films is the presence of an elemental metal plasma above the crucible during the Ag and Cu (but not Al) depositions. This plasma differs from that induced in sputter techniques in several important ways, primarily in that no foreign gas is used. The removal of O by PIB in the Ag/Si case is credited with the ability to achieve thin film sheet resistivities close to the bulk value, a feat not found possible for Al.

Cu deposition on rough ceramic substrate: physical structure, microstructure, and resistivity

Cu films with a thickness around 3.5 μm have been deposited on rough Al 2 O 3 ceramic substrates by the partially ionized beam deposition technique. The substrate temperature during deposition is varied from 50°C to 300°C. Physical structure of the films is studied by SEM in cross-sectional and surface geometries. X-ray diffraction is performed to obtain information on the microstructure of the films. Resistivity of the films is also measured

Impurity effects in partially ionized beam metal via filling

One of the most outstanding problems in multilevel interconnect technology is the filling and planarization of metals in deep vias and trenches. Due to the shadowing effect, metal via filling with large aspect ratio using conventional deposition techniques is known to be very difficult. A directional deposition technique, known as partially ionized beam deposition (PIB) shows that oxide trenches with an aspect ratio of 3 can be filled wall to wall with Al or an Al–Cu alloy. Unlike conventional deposition techniques, Al films deposited by the PIB technique grow layer by layer and do not develop the usual overhang structure at the top corner of the vias. In this paper, a detailed study on the effects of impurities, either from a poor vacuum condition or from the substrate, on the PIB via/trench filling is presented. It is found that the surface mobility is greatly reduced as the vacuum pressure is increased from 10−4 Pa. It is also shown that the minimum substrate temperature (normally less than 200 °C) req...